I have a 91 ski supreme with a closed bow that I am looking to get some weight in for a bigger wake. There is not much interior room so thought about a launch pad seat in the back? Is this good or is it better to weight the sides to sink more of the boat?

I'm not familiar with your boat, but since its closed bow and 19 ft. like mine, start with what Dave said, weight the sides of the engine. My first set up had side sacks (350s) on each side, but I now use 550s on each side. If you go this route, you don't really have to worry about weighting the bow as much.